The First Record of Marenzelleria neglecta and the Spread of Laonome xeprovala in the Danube Delta-Black Sea Ecosystem

Biological invasions can have major impacts on freshwater and marine ecosystems. Therefore, it is vital that non-indigenous species are accurately identified and reported when potential or confirmed invasions occur. The present study reports the first occurrence of Marenzelleria neglecta (Annelida, Spionidae) and the spread of Laonome xeprovala (Annelida, Sabellidae) in the Danube Delta-Black Sea ecosystem. Spionidae is one of the most diverse families of annelid worms and is a dominant group in terms of the number of species that have been introduced to non-native areas, while the members of Sabellidae are among the most visible polychaetes commonly found in fouling communities and are colonizing new geographic areas. Based on 20 samples collected in 2021, we provide an overview of the distribution of the investigated species and possible arrival pathways for Marenzelleria neglecta. Specimens were identified based on morphological descriptions. Both species have invasive behaviour, colonizing large areas in relatively short time periods and reaching relatively high densities (M. neglecta-1400 ind.m(-2); L. xeprovala-40 ind.m(-2)). Due to their distribution and high abundances, the biology and ecology of these species in the Danube River-Danube Delta-Black Sea system need to be investigated further in order to assess their impact on ecosystem structure and functioning.